Hi,
:smileyhappy:
No need to do it in the welcome page...u need to do it in the captive portal - top level login page)
just build a normal login page (html basic) in order to auth in front of your radius (if help in this needed ...tell me)
and to that login page your are building - u may add a simple java script(works almost on all os / devices)
Info on how to build/script the right login page:
http://community.arubanetworks.com/aruba/attachments/aruba/arubaos-and-mobility-controllers/11/1/customize-captive-portal.pdf
This site will give u the script u looking for:
http://lab.artlung.com/validate-checkbox/
have a lovely evening.
me